Data compressing/decompressing technologies for compressing amounts of data without losing contents of original data strings and for decompressing compressed data to recover original data strings have been conventionally developed. One of such technologies is a run length system. In a run length system, when identical specific data pieces consecutively appear, the data pieces are encoded using a data type and a consecutiveness length of the data in a pair, and thus, the consecutive data pieces are compressed.
In a run length system, when compressed data is decompressed with a high operating frequency, a method in which a run length value is expressed by a fixed length is generally used. However, compression efficiency in a fixed-length system may be deteriorated when the number of consecutive data pieces is considerably great or considerably small. Thus, a compressing device has been proposed which improves compression efficiency by using a plurality of formats of compressed data as appropriate according to the number of consecutive data pieces.
However, in a case where the throughput (the number of data pieces which are decompressed in one cycle) of a decompressing device needs to be ensured, analysis of a plurality of run-length data pieces in one cycle is required for data compressed by a compressing device disclosed in prior art. Accordingly, addition and comparison need to be executed many times during one cycle processing, and hence, the reduction in operating frequency becomes a problem.